Note that background is a
shorthand for multiple
background-* properties, with background-color being the first one.

Also keep in mind that you cannot combine the selectors like this:

::selection, ::-moz-selection {
color: white;
background: purple;
}

This will fail because browsers ignore CSS
rules that they consider to have
invalid selectors. Chrome won’t recognize the prefixed version, and Firefox
won’t recognize the unprefixed version, so they both reject the rule.

Browser Support

You should include the -moz- prefixed version for now to support Firefox, but
be aware that Firefox won’t need the
prefix from version 62
onward.

According to Can I use, about 85% of
users are on browsers that support this feature. iOS Safari is the notable
holdout.

Specific Styling

The previous example applies the changes to the entire page, but you can also
limit them to specific elements using standard selectors.